In this work, adsorption of reactive azo dye on pumice has been studied by using batch techniques. The influence of agitation, initial dye concentration, and adsorbent mass has been studied. The equilibrium adsorption capacity of pumice for dye was obtained by using linear Freundlich isotherm. It was found that pumice could be an appropriate adsorbent in removal of dye from wastewater. In order to explain the adsorption mechanism, a diffusion model was applied, and calculations were made for solid diffusivity, (D_s) and external mass-transfer coefficient (k_f). The applied diffusion model showed that kf was constant for all initial dye concentrations (c_o), and D_s increased as c_o did. Furthermore, D_s was found to decrease with increasing adsorbent mass.